Output Function :: Programming GUIs (Creating Graphical User Interfaces)

Creating Graphical User Interfaces

Output Function

The output function returns output arguments to the command line. This is particularly useful if you want to return a variable to another GUI. For an example, see Example: Using the Modal Dialog to Confirm an Operation.

GUIDE generates the following lines of code in the output function:

% --- Outputs from this function are returned to the command line.
function varargout = my_gui_OutputFcn(hObject, eventdata, 
handles)
% Get default command line output from handles structure
varargout{1} = handles.output;

If the GUI is not blocking -- in other words, if the M-file does not contain the command uiwait -- the output is simply the handle to the GUI, which is assigned to handles.output in the opening function.

To make the GUI return a different output -- for example, if you want it to return the result of a user response, such as pressing a push button -- do the following:

Add the command uiwait; to the opening function to make the M-file halt execution until a user activates a component in the GUI.
For each component of the GUI where you expect a user response, make the callback update the value of handles.output, and execute uiresume.

For example, if the GUI contains a push button whose String property is 'Yes', add the following code to its callback to make the GUI return 'Yes' when the user presses the push button:

handles.output = 'Yes';
guidata(hObject, handles);
uiresume;

See the section Managing GUI Data with the Handles Structure for more information about passing data with the handles structure.

When the GUI is called with the command

```
OUT = my_gui
```

and a user presses the Yes push button, the GUI returns the output
OUT = 'Yes' to the command line.

The output varargout, which is a cell array, can contain any number of output arguments. By default, GUIDE creates just one output argument, handles.output. To create a second output argument, add the command

```
varargout{2} = handles.second_output;
```

to the output function. You can set the value of handles.second_output in any callback and then save it with the guidata command.

If you want, you can choose more descriptive names than output or second_output for the fields of the handles structure corresponding to the output arguments.

Opening Function Callbacks